Gaseous and Liquid State Terminal Questions with Answer NIOS

Gaseous and Liquid State Terminal Questions with Answer NIOS National Institute of Open Schooling | NIOS

Gaseous and Liquid State Terminal Questions with Answer NIOS

National Institute of Open Schooling (NIOS)
Sr. Secondary, Module-3
Lession-5: Hydrogen and s Block Elements Terminal Questions with Answer


1. Draw the graphs of the following-
i. p vs V at constant T and n
ii. 1/V vs p at constant T and n
iii. T vs V at constant p

P vs V, P vs 1/V and V vs T graph

2. What is the volume occupied by one mole of a gas at STP (0°C, 1 bar pressure)?

The volume occupied by one mole of gas at STP is equal to 22.4L.

3. The volume of a sample of a gas is 500 mL at a pressure of 1.5 atm. If the temperature is kept constant, what will be the volume of that gas at (i) 1 atm. (ii) 5.0 atm.

P/p = V/v
1/1.5 = V/500
V = 750 mL at 1 atm pressure.
At 5atm pressure-
5/1.5 = V/500
V = 150 mL

4. List the wrong assumptions of kinetic theory of gases which led to van der Waal's equation.

Two of the postulates of kinetic molecular theory of gases were considered wrong due to which Van der Waal's equation came into action-
A. The volume occupied by the gas molecule is negligible in comparison to the total volume of the gas. This postulate is nearly valid if the pressure is low.
B. The molecules do not exert any force of attraction upon one another. This postulate is nearly valid when the pressure is low and the temperature is high.

5. What is the standard temperature and pressure?

The standard temperature in degree centigrade is zero and in kelvin scale is 273.15.
The standard pressure is one atm or one bar.
1 bar = 1.00000 × 105 Pa
1 atm = 1.01325 × 5 Pa

6. What is the lowest possible temperature?

The lowest possible temperature is the absolute value of temperature which is equal to −273oC.

7. CO2 can not be liquefied at 35ºC, however large the pressure may be, Why?

Gasses can liquify only below their critical temperature. CO2 can not liquify at 35oC because its critical temperature is 31ºC.

8. A sample of nitrogen gas weighing 9.3 g at a pressure 0.99 atm occupies a volume of 12.4 litres when its temperature is 55K. What will be its volume when the temperature is 220 K? Assume pressure is kept constant.

Initial pressure = Final pressure = 0.99 atm = P1
Initial volume(V1) = 12.4 litres
Final volume(V2) = To find out
Initial temperature(T1) = 55K
final temperature(T2) = 220K
Thus, by applying the following law we can obtain the final volume-
P1V1T1 = P2V2/T2
(0.99 × 12.4)/55 = (0.99 × V2)/220
or, V2/ = 49.6 litres.
Thus, volume will be49.6 litres at 220k.

9. Calculate the volume of one mole of oxygen at 27oC and 2 atm pressure, given that the volume of oxygen at STP is 22.4 litres.

Pressure of the gas(P) = 2 atm
Temperature(T) = 27 + 273 = 300K
Number of moles(n) = 1
Thus, by applying the ideal gas equation, we get-
PV = nRT
2 × V = 1 × 8.314 × 300
V = 1247.1 litres.

10. What is the Maxwell-Boltzmann Law?

At a particular temperature, different gas molecules posses different velocity. Due to continuous collisions among the gasses molecules and wall of the container, some gas molecules speed up while some gas molecules slow down. Maxwell and Boltzmann observed that a fraction of molecules possesing particular velocity at particular temperature. This is the Maxwell-Boltzmann Law.

11. Explain the following properties of liquids on the basis of their structure:
(i) Volume (ii) Shape (iii) Compressibility (iv) Ability to flow.

i. Volume: Liquid have a definite volume and take the shape of the container in which they are kept. It is not compressible and has the ability to flow because, the force of attraction is strong enough to keep the molecules flow within a boundary.
ii. Shape: Liquid have definite volume but not the sahpe. They take the shape of the container in which they are kept.
iii. Compressiility: Liquids are compressible to a small extent at very high pressure.
iv. Abiloty to flow: In a liquid, particles are not very tightly bound to each other and they have high intermolecular spaces between them, which allows the particles to move or flow.

12. Why diffusion can occur in liquids. Explain.

Diffusion is the motion of a substance from an area of higher concentration to an area of a lower concentration. Diffusion occurs in liquids because particles can move around each other and they are evenly mixed.

13. Define (i) vapour pressure and (ii) boiling point.

i. Vapour Pressure: Pressure exerted by vapour on the surface of liquid is called vapour pressure. It is also called equilibrium vapour pressure. It increases with the increase in temperature and is inversely proportional to the intermolecular forces of attraction. Pure liquid has a greater amount of vapour pressure than the vapour pressure of the solution.
ii. Boiling Point: Boiling point is the point at which the pressure exerted by the vapour becomes equal to the atmospheric pressure and the liquid starts boiling.

14. Differentiate between evaporation and boiling.

Evaporation is the slow process of a state change from the gaseous form. Boiling is the fast and continuous process of heating the liquid.
The main difference is that evaporation takes place from the surface of the liquid and boiling takes place from all parts of the liquid. Evaporation takes place at all temperatures and boiling takes place at a fixed temperature on heating.

15. Explain the effect of temperature on vapour pressure of a liquid.

Vapour pressure is directly related to temperature, it increases with increase in temperature and vice-versa as the temperature of the liquid increases, the kinetic energy of the molecule also increases and as the kinetic energy increases the number of molecules transforming into vapour increases, thus increasing the vapour pressure.

16. Define surface tension and give its CGS and SI units.

Surface tension is the property of the fluid to occupy the minimum surface area possible.
The SI unit of surface tension is Newton per meter or Nm−1.
The cgs unit of surface tension is dyne per cm dyne cm−1.

17. What is surface energy?

Surface energy is the potential energy of the liquid molecules that will help the molecules to remain at the surface of the liquid. All the molecules at the surface try to reach the bottom layer, which will decrease the surface energy. Surface energy is the amount of work done to increase the surface area of the liquid surface.
Mathematically, the surface energy is the work done per unit area of the liquid surface. Surface energy = work done/area
SI unit of surface energy is Joules per m2 or Newton/metre(N/m).

18. Why is energy required to increase the surface area of a liquid?

We know that surface tension is the property of the fluid to occupy the minimum surface area possible. It is equal to the quantity of force per unit area required to increase the surface of a liquid. Surface energy is the energy needed to raise the surface area of a liquid by a given quantity. These are dependent on the intermolecular interactions and due to the cohesive forces around the surface lead to the formation of a thin layer. The surface energy is the work done to produce a new surface and thereby increasing the surface area.

19. What is the effect of addition of a surface active substance on the surface tension of a liquid.

We know that surface tension is the property of the fluid to occupy the minimum surface area possible. It is equal to the amount of force per unit area which is required to expand the surface of a liquid.  The surface-active substances are also known as surfactants which are accumulated at the surface between aqueous and non-aqueous media. The involvement of a surface-active substance reduces the surface tension of a liquid. The surface tension decreases of the liquid due to the addition of that substance.

20. Why are liquid drops spherical in shape?

Liquid drops are spherical in shape due to the surface tension of water which is caused due to the tendency of water molecules to stick together. The spherical shape is having the least possible surface area due to which it can resist any of the external force in the atmosphere.

21. What are wetting and non-wetting liquids?

The wetting liquids are those in which the adhesive forces are more than the cohesive forces. Adhesion is the property of attachment of a particle with another substance. The liquids in which the cohesive forces are dominant than adhesive forces are called non-wetting liquid.

22. The cohesive forces acting in liquids A and B are C1 and C2 respectively and C1 > C2 Which of them would have higher surface tension.

In both of them C1 would have higher surface tension.

23. Liquid A rises in glass capillary tube. If one drop of it is put on a plane glass surface, would it spread out or not. Explain.

Liquid A rises in the glass capillary due to the wetting nature, when water is taken in liquid tends to rise slightly along the walls of the tube for increasing its area of contact with the glass. When the drop of water is put on the plane glass surface it tends to spread because of the wetting nature of the liquid.

24. A liquid forms a convex meniscus in glass tube. Comment on its nature.

The convex meniscus is obtained based on the non-wetting nature of the liquid. Hence the molecules are strongly attracted to each other rather than to the container.

25. Define viscosity.

Viscosity is a measure of a fluid's resistance to flow. It describes the internal friction of a moving fluid. Viscosity decrease on increasing temperature.

26. What is coefficient of viscosity?

The force of friction between two parallel layers of the liquid is called the coefficient of viscosity. It is constant for a liquid and is dependent on the liquid’s nature, temperature, pressure and distance between the layers of the liquid.
ƒ = η . A (du/dx)
ƒ is force of friction
η is coefficient of viscosity
A is area of contact
du/dx is the velocity gradient between the layers.

27. Give CGS and SI units of coefficient of viscosity.

CGS unit: dyne cm-2 sec. or poise(P).
SI unit: Nm-2 sec. or pa sec.

28. What is the effect of temperature on (i) vapour pressure (ii) surface tension and (iii) viscosity of a liquid?

Vapor pressure of liquid increases with the increase of temperature because, at a higher temperature number of molecules have adequately high energy to control the forces of attraction and escape to form vapour. Surface tension decreases with the increase of temperature because cohesive forces decrease with an increase in molecular thermal activity. Viscosity decreases with the increase of temperature because, increase in temperature increases the average kinetic energy of molecules which multiplies the attractive forces between them.

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